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Technical limitations of Raspberry Pi to record analog bipolar signal with high sampling rate


(@ranjanpal)
Active Member
Joined: 10 months ago
Posts: 16
Topic starter  
I am making use of Raspberry Pi to read analog bipolar signals (like AC current) at sampling rate of more than 1kHz (specifically between 1kHz-20kHz)
 
Till now what I have understood so far is that RPi is general purpose linux based microcontroller and not used to record time stamp signals at high sampling rate (i.e. sampling rate >= 1 KHz).
 
But what exactly are the technical limitations because of which we cant achieve sampling rate with more than 1 KHz.
 
For example, MCP3008 is 10 Bit ADC with max sampling frequency of 200KSps working on SPI (ref: https://components101.com/ics/mcp3008-adc-pinout-equivalent-datasheet).
 
Also, ADS1015 is a 12 Bit ADC with maximum sampling frequency of 3.3Ksps working on I2C (ref https://nettigo.eu/products/sparkfun-qwiic-12-bit-adc-4-channel-ads1015)
 
With this, theoretically I should be able to read data with atleast 1KSps. But even that is tough to achieve in RPi.
 
So if someone could please explain what exactly are the technical drawbacks of the RPi (ex. the processor speed, clock speed, bus speed, data rate, allowable sampling rate), I would be very appreciative.
 
Thank you.

 


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 Hans
(@hans)
Noble Member Admin
Joined: 8 years ago
Posts: 2005
 

When it comes to sampling, I assume the RPI can keep up with the range you suggest.
Think of it this way: it can record regular audio, probably even in stereo, without issue.

Seeing the frequency range you have in mind, you may even consider using a audio USB device.
And unlike my previous thought; the RPI should be able to keep up just fine.

See for example this article.


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(@ranjanpal)
Active Member
Joined: 10 months ago
Posts: 16
Topic starter  

Hi,

This is somewhat related to both the above mentioned ADCs. Hence I didnt create a new post.

The datasheet of ADS1015 ( https://www.ti.com/lit/ds/symlink/ads1015.pdf?ts=1607691288335&ref_url=https%253A%252F%252Fwww.google.com%252F ) shows that it has full scale range (FSR) for both positive and negative voltages (Pg13, Table 1)

However, for MCP3008 ( https://cdn-shop.adafruit.com/datasheets/MCP3008.pdf ) I could not get any such clear idea regarding its FSR.

Could you please let me know where is my understanding going wrong ?


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 Hans
(@hans)
Noble Member Admin
Joined: 8 years ago
Posts: 2005
 

I can only guess ... but a 1 KHz sampling rate should be easy to maintain by a Raspberry Pi (I assume).
Then again; maybe others use dedicated hardware to record (for example) audio (up to about 20.000Hz), and maybe that hardware caches by itself?

I'm afraid my experience with ADC's is somewhat limited.

Maybe this StackExchange post explains a few things or provides helpful info?

 


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